docs: improve grid empty state documentation

[tomivirkki]

Description

Fix DX test finding issues related to Grid "empty state" feature:

• Mention that "null" can be passed as the parameter for setEmptyStateText and setEmptyStateContent to clear the empty state content

[sonarcloud[bot]]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
0.0% Duplication on New Code

See analysis details on SonarCloud